The present invention relates to aircraft which transport a suspended load, and also hover while lowering the load, and more particularly to an apparatus for use on an aircraft for accurately controlling orientation of a load.
Helicopters have been found particularly useful in transporting suspended, heavy loads and placing such loads in desired locations. Generally, such heavy lift capacity helicopters are provided with a lift cable which extends from beneath the belly portion of the fuselage for connection to a load. Helicopters have been found particularly advantageous in the erection of bulky and heavy steel transmission towers.
Steel transmission towers are generally constructed of plural, interconnected sections such as an upper section and a lower section. Heavy lift capacity helicopters such as the Sikorsky Sky Crane may be used to suspend and transport the sections. Placement of a lower section is not unduly burdensome because linemen can be positioned on the ground for guiding a suspended lower section into place on a mounting pad. Guy lines can be used to facilitate placement. However, a much greater problem is presented during the lowering of the upper section onto the lower section.
For instance, with the helicopter hovering above the lower section, the suspended upper section will tend to swing and rotate due to changes in wind conditions and also because of the swirling air mass caused by the helicopter's rotating blades. Consequently, it has been found extremely difficult to lower the upper section onto the lower section so that the support legs of the section become aligned. Linemen can be positioned at the top of the lower section for guiding the upper section as it is lowered, but an extremely dangerous situation results because the linemen have no readily available escape route from a twisting and rotating suspended upper section.
Placement of the upper section onto the lower section is effectuated primarily by yawing the helicopter. Thus, it is extremely desirable to have the upper section load respond immediately to helicopter yaw, which is controlled by the pilot. However, it is undesirable to have the load rotate independently of pilot control.
Additionally, it is desirable to permit the upper section to swing independently of helicopter pitch and roll. The helicopter may have to compensate for changes in wind conditions, etc., and such is accomplished by pitching and/or rolling the craft.
Various proposals have been advanced to facilitate the lowering of a suspended upper section. These proposals are directed to maintaining so-called yaw control or control of the suspended load during yaw of the helicopter. However, such proposals have generally utilized a rigid cage assembly suspended beneath the helicopter's fuselage for contacting a spreader bar assembly. Because the cage assembly is rigidly mounted, any pitch or roll of the helicopter will immediately transfer motion to the upper section and undesirably affect its orientation.
Additionally, a rigid cage assembly does not allow the load from the upper section to be directly transferred to the center of lift of the helicopter during forward travel. For instance, as the helicopter gains air speed, the upper section will tend to swing toward the aft end of the helicopter. Because the rigid cage assembly contacts a spreader bar, the load will not be transferred up through the center of lift of the helicopter but rather will be transferred to a position forwardly of the center of lift. This causes the helicopter to assume a pitched down attitude which greatly limits air speed. With a rigid cage assembly, Sky Cranes have been limited to flight speeds of 40 knots or less.
Another problem present in prior art rigid cage assemblies resides in the fact that a helicopter must pitch and roll during hovering in order to compensate for wind changes in the atmosphere as well as swirling wind caused by the helicopter's blades. Rigid case assemblies do not permit the upper section to be suspended in a relatively isolated manner during pitch and roll. In those cage assemblies permitting some degree of freedom in pitch, roll freedom is not necessarily provided.
Accordingly, it is a general object of the present invention to provide a control apparatus for mounting on the fuselage of a helicopter which will directly transmit yaw movement to a speader bar for selectively orienting a suspended load. The apparatus is pivotally mounted on the fuselage in a manner so that pitch and roll movement of the helicopter will not effect orientation of the load. Precise control in yaw is provided and the load will not rotate independently of pilot control.
Another object of the present invention is to provide a control apparatus in which an upper assembly is pivotally mounted to the fuselage about a first pivot axis. A lower assembly is pivotally connected to the upper assembly about a second pivot axis extending transversely to the first pivot axis. A speader bar assembly generally occupying a vertical plane is suspended between the upper and lower assemblies for contact with the lower assembly. Freedom in pitch and roll is ensured while control in yaw is maintained by the lower assembly.
Another object of the present invention is to provide a control apparatus for transmitting helicopter yaw movements to the speader bar, but which permits the line of action of a suspended load to be transmitted directly to the center of lift of the helicopter during forward flight.
These and other objects and advantages of the present invention will be more readily apparent from a consideration of the following drawings and a detailed description of the preferred embodiment.